Slotted waveguide array with parabolic reflectors and lobe switching



June 9, 1964 RAM 3,137,001

M. J. MO SLOTTED WAVEGUIDE ARRAY WITH PARABOLIC REFLECTORS AND LOBE SWITCHING Filed Aug. 25, 1960 TRANSMITTER DUPLE I(ER RECEIVER L 4 /0 24 J w i- AERIAL INVENT E Ml -HAEL JkM E8 NORA-M BY 124 A'T'FYJ'.

7 SLDTTED WAVEGUIDE ARRAY WITH PARABOLIC REFLECTDRS AND LOBE SWITCHlNG Michael James Moran, London, England, assignor to Decca Limited, London, England, a British company Filed Aug. 25, 1960, Ser. No. 51,952 Claims priority, application Great Britain Aug. 25, 1959 7 Claims. (Cl. 343-768) This invention relates to directional aerial systems. In the following description, for convenience and simplicity of terminology, reference will be made more particularly to a transmitting aerial and to radiating slots in a Waveguide. As is well known, transmitting and receiving aerials are analogous and the invention is equally apwaveguide to be propagated along the guide and two series of radiating slots in different faces of the guide, the two series of slots having different amplitude and/or phase characteristics to produce beams in different directions. For example, one series of slots may be an array of phase radiating slots, that is to say, if the slots were fed in phase, adjacent slots would radiate in phase, and the other series of slots may be an array of anti-phased radiating slots, that is to say, if fed in phase, adjacent slots would radiate in anti-phase.

The radiating slots may be in adjacent faces of the guide but generally it will be more convenient for them to be in opposite faces of the guide. A waveguide with slots inopposite faces may be used for example if beams are required in two horizontal directions 180 apart, e.g., in a ground radar system. In such an arrangement reflecting plates extending along the length of the guide and forming flared horns for each series of slots may be provided to give required directional patterns in a plane normal to the axis of the guide. If beams in other directions about the axis of the waveguide are required, suitable reflecting plates may be arranged to guide the radiation from the slots so that the radiations from the two series of slots are in the appropriate required directions in a plane normal to the axis of the waveguide. For example, the radiating slots may be on opposite faces of the waveguide and the reflecting plates may be arranged to guide the radiation from the two series of slots through a curved path through substantially a right angle in a plane normal to the axis of the waveguide so that the signals may be radiated through a common aperture or through two co-planar adjacent apertures forming eflectively a line source. In some cases, as for example described below, the reflecting plates may be arranged to direct the two beams in different directions angularly about the axis of the waveguide.

If the slots are in opposite faces of a rectangular waveguide they may be in the broad or in the narrow faces of the waveguide.

The aerial system in the present invention may be used, for example in a Doppler airborne navigation system of the kind in which two beams are simultaneously radiated downwardly from an aircraft in different directions onto the ground and the reflected signals from the two beams are received in the aircraft and mixed to obtain a Doppler beat frequency. If one beam is directed forwardly and the other rearwardly, the beat note obtained on mixing the signals will depend on the speed of the aircraft relative to the ground. As is well known in such sys- United States Patent terms four beams are generally employed, one directed forwardly to the port side of the aircraft being used with a second beam directed rearwardly to the starboard side and the third beam being directed forwardly to the starboard side and used in conjunction with a fourth beam directed rearwardly to the port side. By using four such beams the ground speed and the actual ground track may be determined. Using the aerial system described above with phased radiating slots on one face and antiphased radiating slots on the opposite face, the slots having the same spacing, identical beams may be obtained, one directed rearwardly and the other forwardly as required for such a Doppler navigational system. Reflecting plates may be arranged so that one of these beams is directed outwardly to the port side of the aircraft and the other directed outwardly to the starboard side of the aircraft. Thus, by feeding the waveguide from one end, two similar simultaneously radiated bems as required for this Doppler navigational system may be obtained. The second pair of beams may be obtained from a second waveguide with two sets of radiating slots. More conveniently, however, both pairs of beams are obtained from one waveguide with two series of slots by arranging the slot conductances in each set to be symmetrical about the midpoint of the guide and by providing switch means so that the waveguide can be fed alternatively from either end. By switching the feed in this manner,

the beam to the port side can be switched from the rearwardly to the forwardly direction and vice versa whilst the starboard side beam would be switched from the forwardly to the rearwardly direction and vice versa. By the use of a suitable duplexing system, the same aerial may be used both for transmission and reception. This arrangement thus enables a single Waveguide with two series of radiating slots and suitable deflecting plates to constitute a complete aerial system for a four beam radio frequency mixing Janus type Doppler aerial navigational system.

The following is a description of one embodiment of the invention, reference being made to FIGURE 1 which is a perspective view of an aerial for a Doppler airborne navigational system;

FIGURE 2 is an end view of the aerial of FIGURE 1;

FIGURE 3 is a block diagram illustrating the connection of the aerial system of FIGURES 1 and 2 to a transmitter and receiver.

Referring to FIGURES 1 and 2, the aerial system has a rectangular waveguide 10 with radiating slots on the narrow faces 11, 12. On the face 11 the slots 13 are arranged as a series of phased radiating slots, that is to say the various slots, if fed in phase, would radiate in phase. On the face 12 the slots 14 are arranged as anti-phased radiating slots, that is to say, if fed in phase, adjacent alternate slots would radiate in anti-phase. The waveguide 10 is supported by supports indicated diagrammatically at 15 between two parallel plates 16 forming a parallel plate transmission line. The plates extend the whole length of the waveguide 10 parallel to the broad faces thereof and are wider than those faces. Along the outer edges of the plate 16 flared portions 17 are provided forming in effect horns for radiating the microwave energy from the slots 13, 14. The two horns constituted by these flared portions 17 feed respectively two parabolic reflectors 18 which deflect the beams from the two faces of the waveguide through an angle about the axis of the waveguide.

In a Doppler airborne navigational system, the waveguide 10 would be mounted with its axis horizontal in the aircraft and would in general be carried on a pitchstabilised mounting, or possibly on a fully stabilised mounting. The narrow faces of the waveguide would be in vertical planes and the reflectors 18 arranged so that the beams are directed downwardly at an angle to the vertical plane with one beam to each side of the aircraft. The axis of the waveguide may be fixed in the fore and aft direction of the aircraft or the aerial mounting may be rotatable so that the axis of the waveguide 10 may be aligned with the actual direction of I travel of the aircraft over the ground. Because the array of slots 13 is phased and the array of slots 14 is antiphased, one of the two beams will be directed forwardly and the other will be directed rearwardly. The two beams will be relatively narrow in the fore and aft direction but wider transversely thereto and, as is well known will, in shape, be like portionsof a cone. Assuming the ground beneath the aircraft is flat, each beam will thus illuminate a strip of ground which is relatively narrow in the direction of travel of the aircraft but is wide in a direction following a hyperbolic curve. The reflectors 18 are arranged so that these beams strike the ground each wholly to one side of a vertical plane through the axis of the waveguide.

The two series of slots 13 and 14 are each arranged to have conductances which are symmetrical about the centre points along the length of the waveguide 10 and switch means are provided so that the waveguide can be fed from either end. The slots 13, when the waveguide 10 is fed from one end, would give a beam directed forwardly and to one side of the aircraft'but would give a beam directed rearwardly and to the same side of the aircraft when the waveguide 10 is fed from the other end. The slots 14 give a beam which is directed always to the other side of the aircraft but this beam would be directed rearwardly when the beam from the'slots 13 is.

is desirable that the other end should be terminated with a suitable matched load. For this purpose, dummy loads 25 are provided and the switches are arranged so that when one end of the waveguide 10 is coupled to the feeder 23'the other end is coupled to one of these loads 25.

I claim: 1. A directional aerial system comprising (a) a length of waveguide having four orthogonal faces, the guide having series of radiating slots in each of two different faces, the two series of slots having different amplitude-phase characteristics to produce beams at different angles with respect to a plane'normal to the axis of the guide, (b) means for feeding radio frequency signals into the waveguide to be propagated along the guide, and

(c) reflecting plates extending along the length of the guide to form flared horns for each series of slots.

'2. A directional aerial system as claimed in-claim 1 wherein one series of slots is an array of ,phased radiating slots and the other series of slots is an array of antiphased radiating slots.

3. A directional aerial system comprising a length of waveguide having four orthogonal faces with two series of radiating slots in opposite faces, the two series of A 5 slots having different amplitude-phase characteristics, a pair of parallel conductive plates arranged to form a parallel plate transmission line with the waveguide between the plates and the radiating slots in faces of the waveguide normal to the planes 'of said plates, and flares on the edges of said parallel plates.

4. A directional aerial system as claimed in claim 3 wherein said flares are arranged to form radiating horns each feeding a parabolic reflector;

5. A directional aerial for a Doppler airborne navigation system comprising a length of rectangular waveguide with two series of radiating slots in opposite faces,

. one series of slots being an array of phased radiating slots and the other series of slots being an array of antiphased radiating slots andfrefiectors arranged to guide therradiation from said slots through angles less than a right angle so that, when thewaveguide has its axis horizontal with the radiating slots in vertical faces, the radiation is deflected downwardly in divergent directions away from a vertical plane through the axis of the waveguide.

6. A directional aerial system as claimed in claim 5 wherein, in each series, the slotshave symmetrical conductances about the centre of the series and wherein means are provided for connecting a feed system alternatively to either end of said waveguide.

7. A directional aerial system comprising (a) a length of waveguide having two orthogonal faces, the guide having a series of slots in each of two different faces, the slots in each series having symmetrical conductances about the center of the series, one series of slots being a series of phased radiating slots and the other series of slots being a series of anti-phased radiating slots to produce respectively beams divergent at angles in opposite directions with respect to a plane normal to the axis of the wavegaide,

(b) means for feeding radio frequency signals to said waveguide alternatively at either end thereof to be propogated along the guide, and

(c) parabolic reflecting plates extending along the length of the guide and arranged to beam the radiation from the two respective series of slots as two separate beams in different directions angularly about the axis of the guide through a common apertore through which the signals are radiated.

References Cited in the file of this patent UNITED STATES PATENTS 2,573,746 Watson et a1. Nov. 6, 1951 2,730,717 Katchky et a1. Jan. 10, 1956 2,764,756 Zaleski Sept. 25, 1956 2,834,014 Thorne May 6, 1958 2,908,904 Van Atta et.al. Oct. 13, 1959 2,911,644 Stavis Nov. 3, 1959 2,932,823 Beck et a1 Apr. 12, 1960 3,039,097 'Strumwa'sser et al. June 12, 1962 3,044,066 Butler 'July 10, 1962 FOREIGN PATENTS 511,669 Belgium June 14, 1952 691,586 Great Britain May 13, 1953 I 725,386 Great Britain Mar. 2, 1955 1,200,570 France June 29, 1959 

1. A DIRECTIONAL AERIAL SYSTEM COMPRISING (A) A LENGTH OF WAVEGUIDE HAVING FOUR ORTHOGONAL FACES, THE GUIDE HAVING SERIES OF RADIATING SLOTS IN EACH OF TWO DIFFERENT FACES, THE TWO SERIES OF SLOTS HAVING DIFFERENT AMPLITUDE-PHASE CHARACTERISTICS TO PRODUCE BEAMS AT DIFFERENT ANGLES WITH RESPECT TO A PLANE NORMAL TO THE AXIS OF THE GUIDE, (B) MEANS FOR FEEDING RADIO FREQUENCY SIGNALS INTO THE WAVEGUIDE TO BE PROPAGATED ALONG THE GUIDE, AND (C) REFLECTING PLATES EXTENDING ALONG THE LENGTH OF THE GUIDE TO FORM FLARED HORNS FOR EACH SERIES OF SLOTS. 